One issue that may arise, particularly in wireless communication systems, is that of frequency coordination and acquisition. This may be of particular concern in a device that needs to be small, low-power and low-cost, such as in many of today's mobile wireless communication systems. A low-cost, low-bandwidth receiver may need to search over many kilohertz (kHz) of bandwidth to locate a transmission to be received because the receiver's local oscillator (LO) may be even only a few parts-per-million (ppm) off from the transmitter's LO frequency. Combined with temporal ambiguities and/or waveform designs that may push the transmission down toward and below the channel noise in order to meet power spectral density (PSD) limits, the receiver's initial acquisition task may become gargantuan.
For example, a device may be required to be able to acquire an incoming signal with a frequency offset of up to +8 kHz (e.g., 2 ppm oscillator offset at up to 4 GHz). Such a device must, therefore, search within a 16 kHz space for its incoming signal. For practical reasons, the device may need to do this in a short enough amount of time that it is not onerous to the user, who may, for example, be standing in place, aiming the device and waiting for it to acquire a signal.
The most efficient mechanism for achieving frequency alignment is to provide a consistent, precise frequency reference—a pilot tone. There are other mechanisms (e.g., chirps, phase-loop tracking of a phase-variant signal, use of a common reference, etc.), but ultimately they all require more resources, meaning ultimately, more time. Therefore, one would ideally like to have a tone-based frequency acquisition that may acquire frequency in a reasonably short amount of time.